1. Field of the Invention
This invention relates to a driving mechanism for use in an image forming apparatus for driving a photosensitive member and a rotary member provided in the vicinity of the photosensitive member.
2. Description of the Related Art
Heretofore, known is a driving mechanism 200 for use in an image forming apparatus, as shown in FIG. 7. Such a conventional driving mechanism 200 drives, by means of a drum driving motor, a photosensitive drum 4 and rotary members provided in the vicinity of the photosensitive drum 4, such as a cleaning roller 160 for removing toner residuals from the surface of the photosensitive drum 4 and a transfer roller 11 for transferring a toner image formed on the drum surface to a copy sheet. The drum driving motor is interconnected with a rear end part 41axe2x80x2 of the rotary shaft 41xe2x80x2 via a driving joint 50xe2x80x2 connected to the drum motor. Thus, the driving force of the drum motor (not shown) is transmitted to the photosensitive drum 4 by means of a rotary shaft 41xe2x80x2 extending through the photosensitive drum 4, with the rotary shaft 41xe2x80x2 rotating with the driving joint 50xe2x80x2. The rear end 41axe2x80x2 of the rotary shaft 41xe2x80x2 is a part of the rotary shaft 41xe2x80x2 provided at the rear side of the image forming apparatus and has a projection 41cxe2x80x2 extending radially outwardly. The driving joint 50xe2x80x2 is coupled to the rotary shaft 41xe2x80x2 with the driving joint 50xe2x80x2 covering the rear end part 41axe2x80x2 including the projection 41cxe2x80x2. 
The driving force of the drum motor is transmitted from the photosensitive drum 4 to the cleaning roller 160 and to the transfer roller 11 by means of a drum gear 43 provided at an axial end of the photosensitive drum 4 and meshing with a cleaning roller gear 161 provided at an axial end of the cleaning roller 160 as well as with a transfer roller gear 111 provided at an axial end of the transfer roller 11, thereby rotating the cleaning roller 160 and the transfer roller 11 along with the photosensitive drum 4. The drum gear 43, the cleaning roller gear 161, and the transfer roller gear 111 are located on the front side of the image forming apparatus and respectively co-rotatably coupled with or attached to the photosensitive drum 4 and the rollers 11 and 16. Furthermore, the rotary shaft 41xe2x80x2 is co-rotatably coupled with the photosensitive drum 4 with a front end part 41bxe2x80x2 of the rotary shaft 41xe2x80x2 being fitted in a hole formed in the axially front end part of the photosensitive drum 4. The front end part 41bxe2x80x2 has a generally D-shape in cross section or its equivalent and is at the axially front end thereof, the hole has a cross-sectional shape to match with the cross-sectional shape of the front end part 41bxe2x80x2. 
The rotary shaft 41xe2x80x2 may be inserted into a hollow portion of the photosensitive drum 4 with the front end part 41bxe2x80x2 of the rotary shaft 41xe2x80x2 being inserted to the hollow portion from the rear side of the image forming apparatus (from the left side in FIG. 7). When the rotary shaft 41xe2x80x2 is fully inserted, its front end 41b project out of the photosensitive drum 4, with the rear end 41axe2x80x2 having the projection 41cxe2x80x2 being located at the rear side to oppose the driving joint 50xe2x80x2. The rotary shaft 41xe2x80x2 and the photosensitive drum 4 are co-rotatably coupled with each other at the front side of the image forming apparatus where the drum gear 43 is in mesh with the cleaning roller gear 161 and the transfer roller gear 111.
Since the rotary shaft 41xe2x80x2 and the photosensitive drum 4 are coupled with each other on the front side of the image forming apparatus at a portion of the front end part 41bxe2x80x2, the driving force is transmitted through substantially the entire length of the rotary shaft 41xe2x80x2 from the rear end part 41axe2x80x2 of the rotary shaft 41xe2x80x2 (rear side of the image forming apparatus) at which the rotary shaft 41xe2x80x2 is jointed to the driving joint 50xe2x80x2, to the front end part 41bxe2x80x2 of the rotary shaft 41xe2x80x2 (front side of the image forming apparatus) at which the rotary shaft 41xe2x80x2 is jointed to the photosensitive drum 4. Then, the driving force of the drum motor is transmitted to the cleaning roller 160 and the transfer roller 11.
Thus, before the driving force of the drum motor is transmitted to the transfer roller 11 and the cleaning roller 160, the driving force is required to be transmitted from the one axial end of the photosensitive drum to the other axial end thereof where a load is applied. Accordingly, it is highly likely that torsional stress may be caused in the rotary shaft 41xe2x80x2 due to a torque necessary for the rotary shaft 41xe2x80x2 to rotate the photosensitive drum 4, the cleaning roller gear 161 and the transfer roller gear 111, during the transmission of the driving force to the cleaning roller gear 161 and the transfer roller gear 111. As a result, the rotational speed of the photosensitive drum 4 may fluctuate.
In view of the above, it is an object of this invention to provide a driving mechanism for use in an image forming apparatus which operates stably.
It is another object of the present invention to provide a driving mechanism which drives a photosensitive drum of an image forming apparatus without fluctuation of rotating speed.
It is still another object of the present invention to provide a driving mechanism which is free from the torsional stress in the driving mechanism.
It is further object of the present invention to provide a driving device for stably driving a photosensitive drum and its related one or more rollers of an image forming apparatus.
It is still further object of the present invention to provide an image forming apparatus including a fixture attaining one or more of the objects as mentioned above.
According to an aspect of this invention, a driving mechanism for use in an image forming apparatus drives a photosensitive member of a substantially cylindrical shape and a rotary member provided in the vicinity of the photosensitive member, the driving member is to be interconnected with a driving motor to be driven thereby. The driving mechanism comprises a rotary shaft extending through the photosensitive member in a longitudinal direction of the photosensitive member and protruding from the photosensitive member at its opposite ends, the rotary shaft being journaled at its axially opposite ends by bearings, and being co-rotatably coupled with the photosensitive member at one of the axially opposite ends thereof, the rotary shaft having a mass larger than that of the photosensitive member; a driving force transmission member which is jointed to the rotary shaft protruding from the photosensitive member at the one of the axial opposite ends, to transmit a driving force of the driving motor to the rotary shaft; a photosensitive member gear provided at the one of the axial opposite ends of the photosensitive member to co-rotate with the photosensitive member; and a rotary member gear provided at the one of the axial opposite ends of the rotary member, the rotary member gear being in mesh with the photosensitive member gear to be driven thereby.
In the above arrangement, the photosensitive member and the rotary shaft are coupled with each other at the side where the photosensitive member gear is in mesh with the rotary member gear and at the lateral side part of the axial end part of the rotary shaft where the rotary shaft is coupled to the photosensitive drum to allow the rotating force of the drum motor to be transmitted via the rotating force transmission member to the photosensitive member. This arrangement shortens a transmission route for the rotating force to be transmitted from the photosensitive member to the rotary member, and thus makes the transmission route shorter than the transmission route of the conventional driving mechanism.
This arrangement dispenses with the mechanism for transmitting the rotating force from one axial end of the rotary shaft and the photosensitive drum to the other axial end thereof before the rotating force is transmitted to the rotary member, as in the case of the conventional structure. Therefore, there is no likelihood that torsional stress may be caused in the rotary shaft during the transmission of the rotating force to the rotary member. Further, since the rotary shaft has the mass larger than the photosensitive member, fluctuation in the rotation of the photosensitive member is effectively eliminated or suppressed, thereby ensuring stable operation of the photosensitive drum and desirable image formation.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawing.